1. Field of the Invention
The invention relates to a hydrostatic planetary rotation machine.
2. Description of the Related Art
Such a planetary rotation machine is described, for example, in EP-A1-761 968. In this machine, the displacer part and the control part are arranged between the shaft bearings for the drive shaft or power take-off shaft passing through both parts. The advantage of this arrangement is that there is a large distance between the bearings, with the result that, in the case of additional radial forces at the outer end of the shaft, for example owing to belt or tooth forces or owing to wheel contact forces, the bearing loads are reduced. A further advantage of this machine is the substantially better mechanically-hydraulic starting efficiency compared with other known systems with the so-called orbital low-speed motors, which generally transmit the torque from the rotary piston to the output shaft by means of a cardan shaft.
However, it has been found that in the known machines, as, for example, according to CH-A5-679062 or EP-A1-0 761 968, a substantial pressure increase and hence power increase compared with the other orbital low-speed engines (high-torque engines) is not possible since the tooth force at the shaft, due to the high hydrostatic force of the rotary piston, results in excessive shaft sags, bending stresses and shear stresses. The bending of the shaft then additionally leads to tooth flank pressure unevenly distributed over tooth width, thus reducing the life of this gear.
It is the object of the invention to improve this machine so that it permits higher operating pressures and hence higher torques and powers compared with the known design while at the same time permitting a smaller number of components.
This results in lower manufacturing costs and a very compact design. A so-called high-torque motor for maximum pressure of about 400 bar and for a continuous pressure of 350 bar is desired. This requirement is associated with the fact that such hydro motors have to be operated with present-day axial and radial reciprocating pumps which are often used as controllable hydrostatic power units. This means that the machine can be designed substantially more robustly and at the same time the volumetric efficiency can be improved.
Although the embodiment of such a motor according to FIG. 4 of EP-Al-0 761 968 already meets this requirement to a certain extent, the embodiment as such-is relatively complicated, as shown further below.
If the roller bearings of that part of the shaft which is subjected to a high hydrostatic radial loadxe2x80x94as also shown in the embodiment according to FIG. 4 of EP-Al-0 761 968xe2x80x94are arranged directly adjacent to one another and a small axial distance apart, the rotary valve must be driven directly by the shaft by means of a toothed gear which permits the rotary valve to rotate exactly and synchronously with the rotary piston of the displacer part. This is indispensable for the commutation of supply to and removal from the working cells of the orbital principle of such machines. In this way, the shaft sag and the skew position of the shaft tooth flanks under load are reduced in an advantageous manner. Furthermore, the shaft tooth system at the displacer part can be made exactly as broad as or even somewhat broader than that of the rotary piston. This was not possible in the case of known machines, as described, for example, in CH-A5-679062 because there a part of the force-transmitting tooth width on the shaft is lost owing to the engagement of the teeth of the connecting shaft from the rotary piston to the rotary valve. The tooth root bending stress and the specific tooth flank load can however be reduced by 15 to 20% by the measure described. A further advantage is the omission of the connecting shaft between the rotary piston and the rotary valve, which accounts for about 3 to 5% of the manufacturing costs.
It is the object of the invention to eliminate the disadvantages which have become evident from the prior art. This is achieved by a toothed gear which is an eccentric internal gear in which a disc-like rotary valve executes an eccentric movement in orbit about a machine axis.
According to the invention, a possible tooth gear is an eccentric internal gear in which the disc-like rotary valve executes the eccentric movement (orbital movement). The two internal gears which form the eccentric gear have differences in the number of teeth between one and two teeth, so that there is multiple tooth engagement, similarly to the displacer tooth system on the displacer part. The tooth shapes used may be cycloid internal tooth systems, in particular trochoidal tooth systems or, where the difference in the number of teeth is two teeth, also involute shaft tooth systems according to DIN 5480 with a 30xc2x0 angle of pressure, if it is ensured that no tooth tip contact disturbances occur.
If the disc-like rotary valve is produced by a powder metallurgical sintering process, no additional manufacturing effort is required for these tooth systems. The tooth system on the shaft can be manufactured in an efficient manufacturing process in one chucking operation together with the shaft tooth system for the displacer part on program-controlled gear-cutting machines. If necessary, this gear wheel can also be mounted nonrotatably on the shaft by means of stamping or sintering. The hollow wheel with the internal tooth system in the housing part on the rotary valve is stamped or broached, it being possible to broach a large number of parts simultaneously. Here too, the manufacturing effort is thus minimized. In order to ensure identical speeds of rotary piston and rotary valve, the numbers of teeth on the tooth system should correspond to the equation                               b          a                ·        d            -      c              d      -      c        =                              x          w                ·        z            -      y              z      -      y      
where a is the number of teeth of the outer tooth system on the shaft, b is the number of teeth of the inner tooth system on the rotary piston, c is the number of teeth of the outer tooth system on the rotary piston, d is the number of teeth of the inner tooth system on the rigid housing part, w is the number of teeth on the first sun wheel on the shaft, x is the number of teeth of the inner tooth system on the rotary valve, y is the number of teeth of the outer tooth system on the rotary valve and z is the number of teeth on the second sun wheel in the form of a hollow wheel fixed to the housing. According to the invention, this equation should express an integer.
In contrast to the known embodiments of planetary rotation machines having a disc-like rotary valve, in the machine according to the invention, as mentioned above, the rotary valve executes a small eccentric movement. This may not adversely affect the proper commutation for the displacer part. It should be kept as small as possible. In the case of the reference diameter given by the overall design for the tooth systems of the eccentric gear, the common eccentricity is all the greater the lower the speed of the axis of eccentricity. Conversely, the speed of the eccentric axis is all the higher the smaller the chosen eccentricity. High speeds of the eccentric axis result in centrifugal forces on the rotary valve, with the result that the tooth systems are loaded and compression losses occur between the inner tooth systems. Preferred tooth system data are given by the value of the equation,   y      y    -    z  
assuming integral negative values between xe2x88x9233 and xe2x88x9255 if, on the eccentric gear, y denotes the number of teeth of the outer tooth system on a disc-like rotary valve and z denotes the number of teeth of the inner tooth system on an adjacent housing or on a second sun wheel in the adjacent housing.
A good compromise between the magnitude of the eccentricity and the speed of the eccentric axis is possible if, with the numbers of teeth a=12, b=14, c=11, d=12 or a=13, b=15, c=12, d=13 of the displacer part, the numbers of teeth of the eccentric gear of the rotary valve can assume the following values:
for (xxe2x88x92w)=1:x=16 to 24; y=29 to 45 teeth
for (xxe2x88x92w)=2:x=31 to 49; y=18 to 46 teeth.
Further, the common eccentricity of the eccentric gear on the disc-like rotary valve is 0.01 to 0.017 times the mean reference diameter of control slots in a control plate.
Finally, the common eccentricity of the two internal gears is 0.011 to 0.015 times the mean reference diameter of the control slots (21) in the control plate.
With these values, the centrifugal forces on the rotary valve are still low, but at the same time the commutation conditions are improved in a large range of angles of rotation of the rotary piston for machine operation with low torque-pulsation and for a good volumetric efficiency.
The differential piston hydraulically compensates the axial forces at the disc-like rotary valve, so that, in both directions of rotation, the leakage gap between the rotary valve and the control plate on the one hand and the rotary valve and the end face of the differential piston on the other hand is reduced to a lubricating film thickness of a few micrometers. In this way, the volumetric efficiency of the machine remains very high even at high pressures and low speeds.